The background description provided herein is for the purpose of generally presenting the context of the disclosure. Work of the presently named inventors, to the extent it is described in this background section, as well as aspects of the description that may not otherwise qualify as prior art at the time of filing, are neither expressly nor impliedly admitted as prior art against the present disclosure.
As an alternative to the internal combustion engine, automotive manufacturers have developed hybrid drivetrains that include both an electric motor and an internal combustion engine. During operation, vehicles including the hybrid drivetrain use one or both of the power sources to improve efficiency. Hybrid vehicles include one of a parallel drivetrain configuration, a series drivetrain configuration, and a combined drivetrain configuration.
In a parallel hybrid vehicle, the electric motor works in parallel with the engine to combine the power and the range advantages of the engine with the efficiency and the electrical regeneration capability of the electric motor. In a series hybrid vehicle, the engine drives a generator to produce electricity for the electric motor, which drives a transmission. This allows the electric motor to assume some of the power responsibilities of the engine, thereby permitting the use of a smaller and more efficient engine.
In a combined hybrid vehicle, the power paths from the engine to the transmission may be either mechanical or electrical. Additionally, for all described hybrid configurations, the engine may be turned off while the vehicle is stopped and a brake pedal is pressed to conserve fuel. Increasing the duration of engine stoppage while the vehicle is at rest increases the hybrid fuel economy benefit.
The hybrid drivetrain may operate in various modes. Operating modes may include a mode where both the engine and the electrical motor drive the transmission. Operating modes may further include a mode where only the electric motor drives the transmission and a mode where the electric motor charges an associated battery.
A conventional hybrid control system determines the operating mode of the hybrid drivetrain based on a power loss of the hybrid drivetrain. The power loss is a total amount of power lost by components of the hybrid drivetrain (e.g., the engine, the motor, the transmission) via, for example, friction and/or heat. While this approach has a positive impact on the fuel economy of the vehicle, drivability of the vehicle may be adversely affected. For example, volatile power loss may cause excessive shifts in the operation mode.